Genes and Behavior: A Twin Legacy
Biology may not be destiny, but genes apparently have a far greater influence on human behavior than is commonly thought. Similarities ranging from phobias to hobbies to bodily gestures are being found in pairs of twins separated at birth. Many of these behaviors are "things you would never think of looking at if you were going to study the genetics of behavior," says psychologist Thomas J. Bouchard, Jr., director of the Minnesota Center for Twin and Adoption Research at the University of Minnesota.
Bouchard reports that so far, exhaustive psychological tests and questionnaires have been completed with approximately 50 pairs of identical twins reared apart, 25 pairs of fraternal twins reared apart and comparison groups of twins reared together. "We were amazed at the similarity in posture and expressive style," says Bouchard. "It's probably the feature of the study that's grabbed us the most." Twins tend to have similar mannerisms, gestures, speed and tempo in talking, habits, and jokes.
Many of the twins dressed in similar fashion - one male pair who had never previously met arrived in England sporting identical beards, haircuts, wire-rimmed glasses and shirts. One pair had practically the same items in their toilet cases, including the same brand of cologne and a Swedish brand of toothpaste.
Although many of the separated pairs had differing types of jobs and educational levels, the investigators are finding repeated similarities in hobbies and interests - one pair were both volunteer firefighters, one pair were deputy sheriffs, a male pair had similar workshops in their basements and a female pair had strikingly similar kitchen arrangements.
Bouchard doesn't have enough information on abnormal behavior or psychopathology to make generalizations, but he has found repeated similarities. One pair of women were both very superstitious; another pair would burst into tears at the drop of a hat, and questioning revealed that both had done so since childhood. "They were on a talk show together and both started crying in response to one of the questions," says Bouchard.
The most striking example of common psychopathology, however, came from a pair of fraternal twins reared apart. One had been reared by his own poor family; the other had been adopted into a "good solid upper - middle-class family." Both are now considered to be antisocial personalities, suffering from lack of impulse control, and both have criminal histories. Although fraternal twins share, on average, 50 percent of their genes, Bouchard suggests that the overlap is probably considerably more with this pair.
Personality similarities between the identical twins reared apart are almost as pervasive as they are with identical twins reared together, according to the results of a test developed by University of Minnesota psychologist Auke Tellegen. His personality questionnaire contains scales such as "social closeness", " harm avoidance" and "well-being". The researchers were especially surprised to find that "traditionalism" - a trait implying conservatism and respect for authority - can be inherited. In fact, says Bouchard, his and other studies have found about 11 personality traits that appear to have significant genetic input.
Overall the emerging findings of the Minnesota study constitute a powerful rebuttal to those who maintain that environmental influences are the primary shaping forces of personality. The textbooks are going to have to be rewritten, Bouchard predicts.
Plentiful food has made it easier than ever before to survive and reproduce in many parts of the world, so it's tempting to think that our species has stopped evolving. But a controversial new study says that isn't so .Far from slowing down, human evolution has sped up in the past 40,000 years and has become 100 times faster in the past 5,000 years alone, according to the analysis. This means that even though some people have been globe-trotters who interbreed, most humans on different continents are becoming more different, rather than blending together into one genetically homogenous race.
Evolution has accelerated in 1800 human genes, which encompass about 70/o of the human genome. Most of the mutations resulted from dramatic population booms. As populations expand, the number of mutations increases, boosting the chances for a beneficial genetic variant that can improve survival and sweep through a population (in the same way that a large population of insects develops a gene for resistance to a pesticide faster than a small population).
Although the researchers don't know the identity of most of the genes, they say quite a few appear to be responses to changes in diet and a new wave of virulent diseases that swept through human populations as they began farming. Some mutations allow adults to digest starch, fatty acids, and lactose in milk. Others improve the resistance to diseases, such as malaria, AIDS, and yellow fever.